Compressor system for natural gas, method of compressing natural gas and plant using them

ABSTRACT

A compressor system including a driver machine, for example a motor or a turbine, an epicyclic gearbox, and a centrifugal compressor, wherein the driver machine, the epicyclic gearbox, and the centrifugal compressor are connected in train configuration, i.e. the output rotary member of the driver machine is coupled to the input rotary member of the epicyclic gearbox and the output rotary member of the epicyclic gearbox is coupled to the input rotary member of the centrifugal compressor. The gear ratio of the epicyclic gearbox is greater than one, typically much more than one, thus increasing the rotation speed from input to output.

BACKGROUND OF THE INVENTION

Embodiments of the subject matter disclosed herein generally relate to acompressor system for natural gas, a method of compressing natural gasand a plant using such a compressor and/or method.

In the field of Oil & Gas, it is common to compress natural gas.

This happens, for example, in upstream plants wherein the gas comestypically from an oil well or a gas well, and is a mixture that containstypically hydrocarbons in variable proportion and/or hydrogen invariable proportion and/or carbon dioxide in variable proportion; whenthe gas comes from an oil well, the gas need to be separated from oilbefore being compressed.

This happens, for example, in downstream plants wherein the gas comestypically from a pipeline or from another plant (so called “processgas”).

In the field of Oil & Gas, three major industrial process stages (withcorresponding plants) are identified: “upstream”, “midstream” and“downstream”; “midstream” is commonly included in “downstream”.

It is worth noting that in the field of Oil & Gas, treating,particularly compressing, gas is problematic; in fact, for example, gasmay be potentially explosive especially if it contains hydrogen and/orammonia.

The solution to the problem of compression used till now and for a verylong time (i.e. many decades) provides for the use of a driver machine,a parallel-axes gearbox, and a compressor (often a centrifugalcompressor) for compressing the natural gas, all of them in trainconfiguration connection. In FIG. 1, there is shown a general blockdiagram of this known solution: a traditional centrifugal compressor TCCis connected to the output of a traditional parallel-axes gearbox PAGBthat is connected to the output of a traditional driver machine TDR;gearbox PAGB increases the rotation speed from input to output and thisis schematically represented by the different number of arcs at itsinput and at its output.

Although many specific solutions have been conceived in order to getever improving performances, the above mentioned approach has beenmaintained; FIG. 1 highlights that the axes of the input shaft and theoutput shaft of the gearbox are parallel and at a distance from eachother.

SUMMARY

With the aim of achieving further and substantial improvements it hasbeen decided to modify the approach, specifically to modify the train.

Instead of using a parallel-axes gearbox, an epicyclic gearbox waschosen.

Epicyclic gearboxes are known since many years and have already beenused in the field of Oil & Gas; anyway, in this field, they have beenused as devices for reducing rotation speed when driving electric powergenerators. In FIG. 2, there is shown a general block diagram of thisknown solution: a traditional electric power generator TEPG is connectedto the output of a traditional epicyclic gearbox TEGB that is connectedto the output of a traditional turbine TTB; gearbox TEGB decreases therotation speed from input to output and this is schematicallyrepresented by the different number of arcs at its input and at itsoutput; FIG. 2 highlights that the axes of the input shaft and theoutput shaft of the gearbox are coincident.

Although many specific solutions have been conceived in order to getever improving performances, the above mentioned approach has beenmaintained till now.

In the field of Oil & Gas, reliability of the plants provided andinstalled to the client is of the utmost importance. Therefore, thecomponents, including the machines, of these plants are chosen based ontheir reliability and long track record.

A first aspect of the present invention is a compressor system fornatural gas.

According to embodiments thereof, a compressor system for natural gascomprises: a driver machine comprising an output rotary member, anepicyclic gearbox comprising an input rotary member and an output rotarymember, and having a gear ratio greater than one thus increasing therotation speed from input to output, and a centrifugal compressor forcompressing natural gas comprising an input rotary member; the outputrotary member of said driver machine is coupled to the input rotarymember of said epicyclic gearbox, and the output rotary member of saidepicyclic gearbox is coupled to the input rotary member of saidcentrifugal compressor.

Some advantageous features and variants are set out in the following.

Said epicyclic gearbox may be multi-stage and more particularlytwo-stage.

Said epicyclic gearbox may comprise at least two (more particularly atleast three) intermediate shafts transmitting rotation from said inputrotary member to said output rotary member, and integrating or mountingone toothed member or two toothed members of different diameters.

The axes of said at least two intermediate shafts may be arranged torotate around the axis of the input rotary member of the epicyclicgearbox.

Said driver machine may be an electric motor.

Said driver machine may be a gas turbine.

Said driver machine may be a steam turbine.

Said gearbox may be mounted on the driver machine.

Said gearbox may be mounted on foot.

Said gearbox may be mounted both on the driver machine and on foot.

The compressor system may comprise further a single baseplate; in thiscase, said driver machine and said centrifugal compressor are mounted onsaid single baseplate.

Said centrifugal compressor may have a rated power in the range from 2MW to 40 MW.

Said driver machine may comprise two output rotary members; in thiscase, the compressor system comprises an epicyclic gearbox and acentrifugal compressor for each of said two output rotary members.

The compressor system may comprise at least one centrifugal compressorin addition to the one already considered; different arrangements arepossible.

According to a first possibility, said centrifugal compressor maycomprise an output rotary member; in this case, the compressor systemmay comprise further: another gearbox comprising an input rotary memberand an output rotary member, and another centrifugal compressor forcompressing natural gas comprising an input rotary member; the outputrotary member of said centrifugal compressor is coupled to the inputrotary member of said another gearbox, and the output rotary member ofsaid another gearbox is coupled to the input rotary member of saidanother centrifugal compressor.

According to a second possibility, another centrifugal compressor iscoupled between said driver machine and said epicyclic gearbox.

The compressor system may comprise further a variable-speed drive systemcoupled to said driver machine and arranged to vary the rotation speedof said centrifugal compressor.

A second aspect of the present invention is a method of compressingnatural gas.

According to embodiments thereof, a method of compressing natural gasthrough a centrifugal compressor provides that said centrifugalcompressor is driven by a driver machine through an epicyclic gearboxhaving a gear ratio greater then one.

Some advantageous features and variants are set out in the following.

The gear ratio of said gearbox may be in the range from 5 to 20.

Said centrifugal compressor may be operated at a maximum rotation speedin the range from 14000 rpm to 28000 rpm.

Said centrifugal compressor may be operated at a pressure ratio in therange from 1.5 to 40.

Said centrifugal compressor may be operated so to provide an maximumoutput gas pressure in the range from 30 bar to 600 bar.

Said centrifugal compressor may be operated so to treat a maximum gasflow in the range from 1500 m3/hr to 100000 m3/hr.

Considering the output rotary member of said driver machine, said outputrotary member may be used for driving two or more centrifugalcompressors at different rotation speeds.

Said driver machine may be operated at variable rotation speed.

A third aspect of the present invention is a plant, i.e. an upstream ora downstream plant.

According to an embodiments thereof, a plant comprises a compressorsystem for gas and this compressor system comprises: a driver machinecomprising an output rotary member, an epicyclic gearbox comprising aninput rotary member and an output rotary member, and having a gear ratiogreater than one thus increasing the rotation speed from input tooutput, and a centrifugal compressor for compressing gas comprising aninput rotary member; wherein the output rotary member of said drivermachine is coupled to the input rotary member of said epicyclic gearbox,and wherein the output rotary member of said epicyclic gearbox iscoupled to the input rotary member of said centrifugal compressor.

The plant may be of the upstream type, in particular of the offshoreupstream type.

The plant may be of the downstream type.

Said compressor system may comprise one or more of the technicalfeatures set out above.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutea part of the specification, illustrate embodiments of the presentinvention and, together with the description, explain these embodiments.In the drawings:

FIG. 1 shows schematically a prior art solution for compressing naturalgas using a parallel-axes gearbox,

FIG. 2 shows schematically a prior art solution for generating electricpower using an epicyclic gearbox,

FIG. 3 shows schematically the principle of the compressor systemsdisclosed herein according to one embodiment of the present invention,

FIG. 4 shows schematically a first embodiment of the present inventionof a compressor system,

FIG. 5 shows schematically a second embodiment of the present inventionof a compressor system,

FIG. 6 shows schematically a third embodiment of the present inventionof a compressor system,

FIG. 7 shows a schematic side view of a fourth embodiment of the presentinvention of a compressor system,

FIG. 8 shows a schematic side view of a fifth embodiment of the presentinvention of a compressor system,

FIG. 9 shows a schematic side view of a sixth embodiment of the presentinvention of a compressor system,

FIG. 10 shows schematically a seventh embodiment of the presentinvention of a compressor system,

FIG. 11 shows schematically a eighth embodiment of the present inventionof a compressor system,

FIG. 12 shows schematically a ninth embodiment of the present inventionof a compressor system,

FIG. 13 shows a graph corresponding to a reasonable limit for usingparallel-axes gearboxes in combination with gas turbines in accordancewith an embodiment of the present invention in accordance with thepresent invention,

FIG. 14 shows two graphs corresponding to a reasonable limit for usingrespectively parallel-axes gearboxes and epicyclic gearboxes incombination with electric motors in accordance with an embodiment of thepresent invention,

FIG. 15 shows a conceptual flowchart of a method for compressing naturalgas in accordance with an embodiment of the present invention, and

FIG. 16 shows schematically an offshore platform in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

The following description of the exemplary embodiments refers to theaccompanying drawings. The same reference numbers in different drawingsidentify the same or similar elements. The following detaileddescription does not limit the invention. Instead, the scope of theinvention is defined by the appended claims.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with an embodiment is included inat least one embodiment of the subject matter disclosed. Thus, theappearance of the phrases “in one embodiment” or “in an embodiment” invarious places throughout the specification is not necessarily referringto the same embodiment. Further, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments.

FIG. 3 shows schematically the principle of the compressor systemsdisclosed herein.

This compressor system comprises: a driver machine DR, an epicyclicgearbox EGB, and a centrifugal compressor CC for compressing naturalgas.

Driver machine DR comprises a output rotary member DO; the epicyclicgearbox EGB comprises an input rotary member GI and an output rotarymember GO; the centrifugal compressor CC comprises an input rotarymember CI.

It is to be noted that all rotary members in FIG. 3 are shown as shaftsprotruding from the boxes of the respective machines only for an easierunderstanding.

The output rotary member DO of the driver machine DR is coupled to theinput rotary member GI of the epicyclic gearbox EGB; the output rotarymember GO of the epicyclic gearbox EGB is coupled to the input rotarymember CI of the centrifugal compressor CC.

It is to be noted that these couplings are shown in FIG. 3 as dashedlines in order to shown that other devices and/or machines might beconnected between the driver machine DR and the epicyclic gearbox EGBand between the epicyclic gearbox EGB and the centrifugal compressor CC;anyway, according to some typical embodiments of the compressor system,as shown for example in FIG. 4 and FIG. 5 and FIG. 6, no machines areconnected in-between.

The gear ratio of the epicyclic gearbox EGB is greater than one(typically much greater than one) thus increasing the rotation speedfrom input to output; this is schematically represented by the differentnumber of arcs at its input, i.e. the member GI, and at its output, i.e.the member GO; specifically, next to the input rotary member GI there isone arc, meaning low rotation speed, and next to the output rotarymember GO there are three arcs, meaning high rotation speed.

It is worth clarifying that, in an epicyclic gearing, two or more outergears (typically three or more outer gears), called “planet gears”, meshwith a central gear, called “sun gear”. The “planet gears” may be fixedor arranged to revolve around the “sun gear”. When the “planet gears”are arranged to revolve around the “sun gear”, an outer ring gear,called “annulus”, surrounds and meshes with the “planet gears”.

The use of an epicyclic gearbox instead of a parallel-axes gearboxallows to save substantial (lateral) space, particularly in terms offootprint of the compressor system; this is due to the fact to the inputand output axes being inline instead of parallel and laterally spaced.

The use of an epicyclic gearbox instead of a parallel-axes gearboxallows to use a simpler gearbox lubrication system as the lubricationrequirements of an epicyclic gearbox are lower than the lubricationrequirements of a parallel-axes gearbox.

It is to be noted that the principle described above may be embodied inmany different ways. The configuration and design of the specificembodiments are influenced by many factors including, for example, thecomposition and/or the pressure of the natural gas coming from the gaswell or oil well.

The centrifugal compressors to be considered for the present patentapplication in the field of Oil & Gas”, such as those labeled CC, CC1,CC2, CC3, CCA, CCB, CCC in the figures, have typically a rated power inthe range from 2 MW to 40 MW.

For the present invention it is important that, during operation, thecentrifugal compressor rotates at high rotation speed; this is achievedby an epicyclic gearbox with a (relatively) high gear ratio.

According to some embodiments, the gear ratio of the epicyclic gearboxis in the range from 5 to 20. In order to achieve such high gear ratios,multi-stage epicyclic gearing may be used. Two-stage epicyclic gearingmay be a good compromise in terms of radial size, axial size, weight andgear ratio of the gearbox.

According to some embodiments, the epicyclic gearbox comprises at leasttwo intermediate shafts transmitting rotation from the input rotarymember to the output rotary member of the gearbox; each of theseintermediate shafts may integrate or mount two toothed members ofdifferent diameters located at opposite sides of the intermediate shaftso that gear ratio is increased in a limited space; these intermediateshafts may be arranged to rotate around the axis of the input rotarymember of the epicyclic gearbox; more particularly, three or fiveintermediate shafts, symmetrically located around the input rotarymember, are used. The solution of gearbox just described may beconsidered a specific type of two-stage epicyclic gearbox, the twostages being integrated in a single arrangement, and is called “compoundgearing”.

In the embodiment of FIG. 4, an electric motor EM is used as a drivermachine; using electric motor for compressing natural gas is typical ofupstream applications particularly for offshore platforms. Thecompressor system of FIG. 4 comprises the electric motor EM, anepicyclic gearbox EGB1 and a centrifugal compressor CC1 connected intrain configuration.

In the embodiment of FIG. 5, a gas turbine GT is used as a drivermachine. The compressor system of FIG. 5 comprises the gas turbine GT,an epicyclic gearbox EGB2 and a centrifugal compressor CC2 connected intrain configuration.

In the embodiment of FIG. 6, a steam turbine ST is used as a drivermachine. The compressor system of FIG. 6 comprises the steam turbine ST,an epicyclic gearbox EGB3 and a centrifugal compressor CC3 connected intrain configuration.

The choice of the driver machine is influenced by many factors.

FIG. 7 and FIG. 8 and FIG. 9 emphasizes the construction of thecompressor system even if in a very schematic way. These figures do notspecify the kind of driver machine used, and they show simply a drivermachine DR, an epicyclic gearbox EGB and a centrifugal compressor CCconnected in train configuration.

All the embodiments of FIG. 7 and FIG. 8 and FIG. 9 comprises a singlebaseplate BP and provide that the driver machine DR and the centrifugalcompressor CC are mounted on the baseplate BP.

In FIG. 7, the epicyclic gearbox EGB is mounted only on the baseplateBP.

In FIG. 9, the epicyclic gearbox EGB is mounted only on the drivermachine DR.

In FIG. 8, the epicyclic gearbox EGB is mounted partially on thebaseplate BP and partially on the driver machine DR.

It appears from FIG. 7 and FIG. 8 and FIG. 9, that, according to thepresent invention, mounting of the epicyclic gearbox on the centrifugalcompressor is not the preferred choice. In fact, the choice and designof the centrifugal compressor are already difficult and depend on thespecific application and application conditions of the compressorsystem; therefore, it is preferable to avoid complicating further thechoice and design of the centrifugal compressor by considering also theneed of mounting a gearbox on it.

As it is schematically highlighted in FIG. 7 and FIG. 8 and FIG. 9,mounting directly the epicyclic gearbox on the driver machine (typicallyon an electric motor) leads to a very compact arrangement, i.e. with asmall footprint. A double mounting (see FIG. 8) may be a compromisebetween size of the footprint and mechanical complication of the designof the flanges of the driver machine and the gearbox.

The choice of the mounting of the epicyclic gearbox is influenced bymany factors.

Mounting of the gearbox directly on the driver machine allows to savesubstantial (longitudinal) space, particularly in terms of footprint ofthe compressor system.

Other embodiments of the compressor system comprise a number of machineshigher than three connected in train configuration as shown for examplein FIG. 10, FIG. 11, FIG. 12.

In FIG. 10, there is shown an embodiment wherein the driver machine DRcomprises two output rotary members, in particular on opposite sides,and there is an epicyclic gearbox (EGBA and EGBB) and a centrifugalcompressor (CCA and CCB) for each of the two output rotary members; thismay be considered a double-train configuration.

In FIG. 11, the compressor system comprises, in addition to thecentrifugal compressor CC, another centrifugal compressor CCC; in thiscase, the compressor CC has an output rotary member (not shown in thefigure). Another gearbox GB is provided so that the two compressors CCand CCC may rotate at different rotation speeds.

The mechanical connection is a single-train configuration; the rotarymembers of the machines are not shown in the figure. The output rotarymember of the driver machine DR is connected to the input rotary memberof the epicyclic gearbox EGB, the output rotary member of the epicyclicgearbox EGB is connected to the input rotary member of the compressorCC, the output rotary member of the compressor CC is connected to theinput rotary member of the gearbox GB; the output rotary member of thegearbox GB is connected to the input rotary member of the compressorCCC. Comparing FIG. 11 with FIG. 1, one can realize that other machinesare mechanically connected downstream to compressor CC, and as part ofthe same train.

The fluid connection in the embodiment of FIG. 11 provides that the gascompressed by compressor CC is further compressed by compressor CCC;therefore, in general there is no need that the rotation speed ofcompressor CCC is much higher than the rotation speed of compressor CC;therefore, gearbox GB does not need to be an epicyclic gearbox (having ahigh gear ratio), although it might be.

Also in FIG. 12, the compressor system comprises, in addition to thecentrifugal compressor CC, another centrifugal compressor CCC. Anothergearbox GB might also be provided.

The mechanical connection is a single-train configuration; the rotarymembers of the machines are not shown in the figure. The output rotarymember of the driver machine DR is connected to the input rotary memberof the gearbox GB, the output rotary member of the gearbox GB isconnected to the input rotary member of the compressor CCC, the outputrotary member of the compressor CCC is connected to the input rotarymember of the epicyclic gearbox EGB; the output rotary member of theepicyclic gearbox EGB is connected to the input rotary member of thecompressor CC. Comparing FIG. 12 with FIG. 1, one can realize that othermachines are mechanically connected between the epicyclic gearbox EGBand the driver machine DR, and as part of the same train.

The fluid connection in the embodiment of FIG. 12 provides that the gascompressed by compressor CCC is further compressed by compressor CC. Therotation speed of compressor CC is much higher than the rotation speedof compressor CCC due to the presence of the epicyclic gearbox EGB;therefore, gearbox GB may also be omitted or, if present (as in FIG.12), gearbox GB does not need to be an epicyclic gearbox (having a highgear ratio), although it might be.

Especially if an electric motor is used as a driver machine in thecompressor system, it is useful to provide in the compressor system avariable-speed drive (VSD) system coupled to the driver machine andarranged to vary the rotation speed of the centrifugal compressor orcompressors. For example a reliable four-poles AC induction electricmotor operating at a frequency of 50 Hz may be combined with a reliableVSD system able to vary the frequency from 0 Hz up to 75 Hz; this resultin a rotation speed from 0 rpm to 2250 rpm.

In the graphs of FIG. 13 and FIG. 14, the Rated power is expressed inMWatts and the Gear ratio is expressed as a pure number.

The graph of FIG. 13, labeled PAGB, has been derived by the Inventorsand corresponds to a reasonable limit for using parallel-axes gearboxesin combination with gas turbines; this graph assumes a rotation speed ofthe gas turbine acting as a driver machine of about 6000 rpm; above thislimit, parallel-axes gearboxes can not be used and epicyclic gearboxeshave to be contemplated.

A similar graph may be provided for steam turbines.

The graphs of FIG. 14, labeled PAGB and EGB, have been derived by theInventors and correspond to a reasonable limit for using respectivelyparallel-axes gearboxes and epicyclic gearboxes in combination withelectric motors; these graphs assume a rotation speed of the electricmotor acting as a driver machine of about 1500 rpm (50 Hz operation);very similar graphs may be provided for a rotation speed of about 1800rpm (60 Hz operation); the best area of application (according to thecurrent technologies) of the combination of a four-poles AC inductionelectric motor and an epicyclic gearbox is comprised between these twographs; it is to be considered that four-poles AC induction electricmotors are certified to be used for very high power applications (forexample 2-40 MW) even in environments with risks of explosions due to aspecific gas mixture being compressed.

It is worth clarifying that, although FIG. 14 refers to use offour-poles motors, the present invention does not exclude the use oftwo-poles motors.

Additionally, it is worth noting that, although FIG. 14 refers to thecompound epicyclic gearboxes (i.e. having a gear ratio greater thanabout 10 or 11), the present invention does not exclude the use of“simple” (i.e. not compound) epicyclic gearboxes when the required gearratio is lower (for example lower than 10 or 11).

The compression of gas in the above described embodiments, is carriedout, at least partially, by means of a centrifugal compressor driven bya driver machine through an epicyclic gearbox having a gear ratiogreater then one.

As shown in FIG. 15, in general, a centrifugal compressor CC is arranged(step 1610) according to an appropriate design and/or choice, a drivermachine DR is arranged (step 1620) according to an appropriate designand/or choice, an epicyclic gearbox EGB is arranged (step 1630)according to an appropriate design and/or choice; by rotating the drivermachine DR (step 1640) also the centrifugal compressor CC is rotated bymeans of the epicyclic gearbox EGB; clearly, the gas is provided to theinlet of the centrifugal compressor CC before starting the drivermachine DR.

The epicyclic gearbox is used for reaching a high rotation speed of thecompressor; therefore, in an embodiment, the gear ratio of saidepicyclic gearbox is in the range from 5 to 20, depending on theapplication; the epicyclic gearbox is designed accordingly.

In an embodiment, the centrifugal compressor is operated at a maximumrotation speed in the range from 14000 rpm to 28000 rpm, depending onthe application; with present technologies, the upper limit is chosen atabout 22000 rpm; the centrifugal compressor is designed accordingly.

A high rotation speed (achieved through epicyclic gearing) allows to usemore compact and more efficient centrifugal compressors.

In an embodiment, the centrifugal compressor is operated at a pressureratio in the range from 1.5 to 40, depending on the application.Although very high pressure ratios are desirable, the mixture of the gasinfluence the choice of the pressure ratio: for example, if a naturalgas is rich of hydrogen, the lower part of the above mentioned range ispreferable due to the risk of explosions.

The centrifugal compressor is operated so to provide an maximum outputgas pressure in the range from 30 bar to 600 bar, depending on theapplication.

The centrifugal compressor is operated so to treat a maximum gas flow inthe range from 1500 m3/hr to 100000 m3/hr, depending on the application.

The ranges of parameters just set out for operating the centrifugalcompressor influence the technical features of the centrifugalcompressor as well as the technical features of the driver machine andthe epicyclic gearbox.

Step 1640 provides to rotate the driver machine of the compressor systemand consequently any centrifugal compressor of the compressor systemconnected or coupled thereto.

The rotation speed is often constant during stable operation, i.e.regime. In an embodiment, the rotation speed is varied, for exampleduring start-up or if different regimes are contemplated; for thispurpose a VSD system is used.

According to some embodiments, there are more than one centrifugalcompressors and the method provides to drive by means of the same drivermachine two or more centrifugal compressors at different rotationspeeds. This is useful for example when driving two cascaded compressionstages.

The above described compressor systems and methods are typically appliedand used in plants of the “Oil & Gas” industry, i.e. in “upstream”and/or “downstream” plants.

FIG. 16 shows an offshore platform OP comprising a compressor system CSfeeding compressed natural gas to a pipeline PL; this is an example ofan “upstream” application. Alternatively, the compressor system CS maybe used at an offshore platform to produce compressed gas, to beinjected into a well.

Very good results have been achieved by combining an electric motor(especially a four-pole electric motor), and epicyclic gearbox(especially a compound epicyclic gearbox) and a centrifugal compressorand using this combination as a compressor system such as the one shownin FIG. 16.

An particular example of a “downstream” application may be thecompression of ammonia.

At the light of the above, a person skilled in the art understands theadvantages of the embodiments just described and the embodiments fallingwith the appended claims.

Some advantages of the centrifugal compressor of the compressor systemaccording to embodiments of the present invention are the following:reduction in the size, improvement in efficiency, reduction in weight,and reduction in footprint.

Some advantages of the driver machine of the compressor system accordingto embodiments of the present invention are the following: possibilityto use lower power driver machines, possibility to use lower speeddriver machines, reduction in weight, and reduction in footprint.

Some advantages of the gearbox according to embodiments of the presentinvention are the following: lower weight, lower size, lower footprint,lower lubrication oil consumption, and higher efficiency (up to 1%).

Some advantages of the baseplate of the compressor system according toembodiments of the present invention are the following: lower size, andlower weight.

A person skilled in the art understands that each of the above listedadvantages applies to distinct embodiments to a different extent.

This written description uses examples to disclose the invention,including the preferred embodiments, and also to enable any personskilled in the art to practice the invention, including making and usingany devices or systems and performing any incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal languages of the claims.

What is claimed is:
 1. A compressor system for natural gas, thecompressor system comprising: a driver machine comprising a first outputrotary member; an epicyclic gearbox comprising a first input rotarymember and a second output rotary member, the epicyclic gearbox having agear ratio greater than one thus increasing the rotation speed frominput to output; and a first centrifugal compressor configured tocompress natural gas, the first centrifugal compressor comprising asecond input rotary member; wherein the first output rotary member ofthe driver machine is coupled to the first input rotary member of theepicyclic gearbox, and wherein the second output rotary member of theepicyclic gearbox is coupled to the second input rotary member of thecentrifugal compressor.
 2. The compressor system of claim 1, wherein theepicyclic gearbox is multi-stage, and/or compound type.
 3. Thecompressor system of claim 1, wherein the driver machine is an electricmotor or a gas turbine or a steam turbine.
 4. The compressor system ofclaim 1, wherein the gearbox is mounted on the driver machine, or onfoot, or on the driver machine and on foot.
 5. The compressor system ofclaim 1, further comprising a second centrifugal compressor configuredto compress natural gas, wherein the first centrifugal compressor andthe second centrifugal compressor are connected in train configurationto the first output rotary member of the driver machine.
 6. A method ofcompressing natural gas through a centrifugal compressor, the methodcomprising: driving the centrifugal compressor through an epicyclicgearbox using a driver machine, wherein the epicyclic gearbox has a gearratio greater than one.
 7. The method of claim 6, wherein the gear ratioof the epicyclic gearbox is in the range from 5 to
 20. 8. The method ofclaim 6, wherein the driver machine comprises an output rotary member,and wherein the output rotary member is configured to drive an at leasttwo or more centrifugal compressors at different rotation speeds.
 9. Themethod of claim 6, wherein the driver machine is operated at a variablerotation speed.
 10. A plant comprising: a compressor system for gas,wherein the compressor system comprises: a driver machine comprising afirst output rotary member; an epicyclic gearbox comprising a firstinput rotary member and a second output rotary member, wherein theepicyclic gearbox has a gear ratio greater than one thus increasing therotation speed from input to output; and a centrifugal compressorconfigured to compress gas, the centrifugal compressor comprising asecond input rotary member; wherein the first output rotary member ofthe driver machine is coupled to the first input rotary member of theepicyclic gearbox, and wherein the second output rotary member of theepicyclic gearbox is coupled to the second input rotary member of thecentrifugal compressor.
 11. The compressor system of claim 2, whereinthe epicyclic gearbox is two stage.
 12. The plant of claim 10, whereinthe epicyclic gearbox is multi-stage, and/or compound type.
 13. Theplant of claim 10, wherein the driver machine is an electric motor or agas turbine or a steam turbine.
 14. The plant of claim 10, wherein thegearbox is mounted on the driver machine, or on foot, or on the drivermachine and on foot.
 15. The plant of claim 10, further comprising asecond centrifugal compressor configured to compress natural gas,wherein the first centrifugal compressor and the second centrifugalcompressor are connected in train configuration to the first outputrotary member of the driver machine.
 16. The plant of claim 10, whereinthe epicyclic gearbox is two stage.